Seven monoclonal antibodies (MABs) against rat neurophysin have been produced and fully characterized. These MABS have been used in developmental studies in the fetal rat hypothalamus. Differential expression of the specific properties of vasopressin- and oxytocin-neurons during development has been found. Two forms of ATPase have been found in the neurosecretory granule (NSG) membrane. One of these appears to be the proton-transporting ATPase. A catalogue of NSG membrane proteins is near completion, and 21 MABs to these proteins have been made. The self-association properties of the AVP-prohormone has been studied, and found comparable to AVP-liganded neurophysin, and much greater than unliganded neurophysin. Several properties of the axon have been studied in the squid axon model. The observations are that axoplasm contains substantial lipid synthesis capacity, litle acid protease, and very high CA++ activated neutral protease activity. The distribution of the Ca++ activated protease indicates that it may be involved in formation of nerve terminals during development.